If you're anything like me, you were using the Warlock's Bloodreaper wrong!
If you look really closely in the Rulebook under "Life +/- X" it is explained that "loss of life" is different from taking damage: loss of life modifies your maximum life total! But the Warlock card doesn't say "Life - X" from the Bloodreaper ability, it just says "loses life equal to Level +1". And thus (If you're like me) you wouldn't even think to look under "Life +/- X", without that handy little note on the Warlock page:
http://www.magewars.com/jsite/detailed-overview/mages/the-warlockTIL. And perhaps so did you.